PROJECT SUMMARY HIV-infected people who inject drugs (PWID) are less likely to engage in HIV care and use antiretroviral therapy (ART) than other groups of HIV-infected people. In HIV Prevention Trials Network (HPTN) 074, an integrated intervention combining systems navigation and psychosocial counseling (SNaP) was highly effective in increasing ART uptake, viral suppression, and medication-assisted treatment (MAT) uptake among HIV- infected PWID. Remarkably, SNaP also reduced mortality. Unfortunately, SNaP, like many evidence-based interventions (EBI), may fail to achieve its full potential at the population level if barriers to implementation with this vulnerable population are not addressed. In this study, we propose to compare two implementation strategies for SNaP?both are based on the concept of Intervention Mapping. Intervention Mapping is a formalized multistep process incorporating theory, evidence, and stakeholder perspectives to select a package of implementation strategies that addresses barriers to EBI implementation. Tailored Intervention Mapping expands upon Intervention Mapping by incorporating site-specific barrier assessment and locally tailored implementation strategies. Our specific aims are: 1) To compare tailored Intervention Mapping (TIM) to standard Implementation Mapping (IM) to scale-up SNaP in 42 HIV test sites throughout Vietnam; 2) To measure the incremental costs of TIM compared to IM for SNaP implementation in Vietnam; and 3) To explore the key characteristics of high and low performing HIV test sites for SNaP implementation in each study arm. In Aim 1, we will conduct a two-arm, pragmatic, cluster randomized controlled implementation trial comparing IM, a standard, one-size fits all multi-faceted implementation package identified through Intervention Mapping, and TIM, a tailored implementation package using Intervention Mapping at both central and local levels. The primary outcomes include fidelity of the SNaP intervention (implementation) and ART uptake (effectiveness). Secondary implementation outcomes include penetration, acceptability, and cost; secondary effectiveness outcomes include viral suppression and MAT uptake. The primary cost-effectiveness outcome (Aim 2) will be the incremental cost-effectiveness ratio, expressed as the incremental cost per incremental ART uptake, comparing TIM to IM. Upon completion of the trial, we will explore characteristics of high and low performing HIV test sites (Aim 3) using both qualitative and quantitative data. This study will provide guidance for the global implementation of the HPTN 074 intervention, SNaP, as well as other EBI. Importantly, this guidance will not depend on the superiority of TIM relative to IM, but will be informative with a positive or a negative comparison. With this information and guidance, the success of HPTN 074 will be replicable worldwide.